It stands for Oh Dear God. It means shock or surprise.
Bob: Bill, I love you. Will you go out with me?

Bill: ODG dude, you have got the hugest spot on your nose. Use some Clearisil!!
by Chenai April 06, 2008
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Already knowing, but being told again! response: "ODG"

I have on a green shirt...hey your shirt is green!!! "ODG"
by Unicornpoo November 13, 2009
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The "Old Dirty G*din." An impressionable young virgin who gets his naked ass smacked with his own belt by a filthy sloppy rolly polly girl on "amateur" night at the local dive. Following the encounter he tells the audience he "could've had her," forever shedding his innocent skin and becoming the ODG. He goes home a new man. She goes home to spread her herpes with whomever says "hello" to her next.
After Ryan saw his first live naked girl, he turned into the ODG.
by Bartender at the Zoo December 01, 2006
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